NON-HYDROGEN ISOTOPE EFFECT ON STRUCTURAL PHASE-TRANSITION IN DIELECTRIC CRYSTALS

Recent observations on the non-hydrogen isotopic effect shed new light on the nature of the displacive type and order-disorder type ferroelectric phase transitions in dielectrics. The isotopic effect on T(c) is discussed in relation to the hydrostatic pressure effect on T(c) and the band-gap shifts induced by transitions. It is shown that these phenomena are strongly correlated in these types of transition. Also, it is concluded that the displacive-type transition is due to the quantum-mechanical electron-phonon interaction in those crystals.